Cooling system for vacuum tubes



Aug. 28, 1945. w c. iwDD 2,383,620

COOLING SYSTEM.FOR VACUUM TUBES I ,Filed Ma 27, 1943 I 1 21 5' Y 4 1 f20 2%; PRE $JUEE CONTROL SWITCH TEMPERATURE CONTROLLED FLOW /16 CONTROLDISCHARGE j' *4; 7' i i J is r l 1 I I 12 K M ENTOR.

Mal, M

A omvEl Ls'.

' Patented Aug. 28, 1945 2.383.020 COOLING srs'rnu Foa VACUUM TUBESWallace 0. Rudd, Yonkers, N.-Y., asslgnor to Inductlon Heating Corp.,poration of New York Application May 27, 1943, Serial No. 488,664

Claims.

This invention relates to cooling systems for vacuum tubes and the like.

In order to cool vacuum tube apparatus such as power oscillator tubes,it isthe common practice to connect th cooling fluid cavities directlywith a municipal or public water supply. the water flowing to wasteafter passing from the tubes. This method involves severaldisadvantages, First, the large amount of water necessary becomes costlyif the tubes are in use continuously for considerable periods of time,particularly in localities where the available water supply is limited.Also the water supply may vary rather widely from moment t moment due tothe opening and closing of water taps at adjacent points on the watersystem, thus causing variations in pressure and consequent seriesvariations in the rate of flow through the tubes. With power vacuumtubes it is important to maintain a predetermined rate of flow of thecooling water. Otherwise, the tubes may be quickly injured due tooverheating. While it is possible to utilize flow control switches toshut off the electric power supply when the rate of flow falls belownormal, and thus protect the tubes against injury, yet if sensitive flowswitches are used for that purpose and thewater pressure fluctuatesconsiderably, then the operation of the tubes will be liable to frequentinterruption under the control of the flow switch. Where vacuum tubessuch as power oscillators are being used for purposes such as inductiveheating, such interruptions may make it necessary to discard objectsbeing heat-treated because of uncertainty as to the extent of the heattreatment. Thus even momentary fluetuatlons in the pressure of the watersupply may involve a troublesome chain of events. Also generally similardifiiculties are involved in case the water supply is entirely cut ondue to breakage of city supply lines or when the connections thereforare being altered.

The present invention provides a system for overcoming the above noteddifiiculties. In accordance with this invention, means are provided formaintaining a substantially constant pressure and flow of the coolingwater through the vacuum tubes and at the same time a, system which maybe kept in operation for at least a considerable period even though thecity water supply is interrupted or varies widely in pressure.

Various further and more specific objects, features and advantages willappear from the detailed description given below taken in connectionwith the accompanying drawing which forms a part of this specificationand illustrates merely even momentarily,

New York, N. Y., a corby way of example, a preferred form of theinvention. The invention consists in such novel combinations of partsand method steps as may be shown and described in connection with theThere are tw principal factors which determine the required minimum rateof flow of cooling water through vacuum tubes. The first and generallymost important factor is that the velocity of flow should be greatenough so that steam bubbles will not form in the water at the surfacesto be cooled. This is important because the formation of such steamwould serve to insulate the hot surfaces from the cooling water and thusquickly result in destruction of the tubes. Another factor generally oflesser importance is that the cooling water as supplied rbe sufiicientin quantity considering its temperature, to absorb the amount of heatwhich is to be dissipated in protecting the apparatus, When the coolingfluid conduits of the tubes are connected directly to the city watersupply as heretofore, the controlling factor in determining the rate atwhich the water supply is used, has been the matter of maintaining therequiredvelocity through the tubes. That is, except for the requirementof maintaining arelatively high velocit, the amount of water used couldbe considerably reduced even though the tubes might become heated tosomewhat higher operating temperatures than have been customary.

The present invention provides an arrangement for maintaining therequired high velocity of cooling water, at a value substantially thesame as with the practice heretofore, but at the same time aconsiderable proportion of the water supply is recirculated and thusreused so that the amount of water which has to be purchased is greatlyreduced. At the same time the recirculation system is designed tomaintain a substantially constant pressure and rate of flowindependently of fluctuations in the city water supply- In the exampleof the invention shown in the drawing, an elongated tank in ofsubstantial capacity, for example 5 gallons, is shown having an intakepipe ll adapted to be connected through adjustable valve l2 to a citywater supply. A discharge pipe I3 is provided at the other end of thetank remote from the inlet, for northe pump to the tubes may ture in theneighborhood of 85 F. assuming the water through the tubes,

mally discharging water at substantially the same rate as suppliedthrough the inlet. With the particular apparatus shown, for example,this intake and outlet rate may be from 1 to 2 gallons per minute, ascontrasted with a rate of 4 to 6 gallons per minute required when thecity water supply is passed directly through the cooling conduits of thetubes. 1

A small circulating pump is shown at l5, driven for example by a motorIS. The inlet conduit it of this pump may be connectedat l'l into thetank III at a region preferably near and below the tank inlet pipe H..The outlet conduit l8 from the pump it may be connected to a pressurecontrolled switch l8 hereinafter described, and thence by insulationconduit means 20 to the inlet 2| oi the cooling fluid cavities of avacuum tube 22. In the particular example shown, the vacuum tubescomprise a pair of #892 three-electrode power oscillators 22, 22'. Fromthe water outlet of tube 22 the cooling water may pass through aninsulation conduit 23 to the water inlet for tube 22'. From the wateroutlet of tube 22' the water may be conducted through an insulationconduit 24 to a flow controlled switch 25 hereinafter described, andthence by a conduit 26 to a point in tank l near the tank outletconnection ii. In order that the vacuum tubes will not be grounded bythe stream of water flowing through conduits 20 and 24, these insulationconduits may be made oi considerable length and if desired, partiallyformed into coils as at 20' and 24.

In the particular example shown, the pump it and associated circulatingconduits are arranged to circulate water from and back to the tank illat the required rate of from 4 to 6 gallons per minute to insure thesame velocity of flow through the tubes as with the practice heretofore.This is suflicient, but not very substantially greater than required toprovide the necessary velocity through the tube cooling cavities forpreventing formation of steam bubbles therein. It will be noted thatheat from the circulated cooling water is eiiiciently transferred to thewater flowing into and out of the tank ill by mixing directly therewith.And since the pump intake is located near the intake for the supply ofcool water, and the return conduit 26 is connected near the hot wateroutlet from the tank, the-maximum practically possible transfer of heatfrom the circulating water to the water entering and leaving the tank isassured.

In the example shown, the water supplied from be of a temperacity watersupply is at a temperature for example of 50-60 F. The water as returnedfrom the tubes to the tank may be at a temperature in the neighborhoodof 110 F. With the practice heretofore, such vacuum tubes were commonlyoperated at maximum temperatures of from 55- 90 F. Such relatively lowtemperatures were not necessary for protection of the tubes, but

the necessity of mainof flow of the cooling for the reason aboveexplained. The operation at a temperature of say 110 F., with thepresent invention is however still well below the permissible maximumoperating temperature of tubes of this type (about 150 F.) and yetgenerally makes possible a saving of well more than two-thirds of therequired water expense, The flow at a rate were brought about by taininga high velocity .of one or two gallons per minute into and out of thetank or reservoir I0 is ample to norma prevent rise of the tank wateroutlet temperature above a safe tube operating temperature of 110 F. forexample.

At the same time the circulating pump arrangement insures that thepressure of the water supply to the tubes will remain substantially freeof fluctuations, as will consequently also the rate of flow andvelocity. Furthermore, if the city water supply should be cut off, for aconsiderable period thereafter the circulating pump may be kept inoperation and maintain proper cooling of the tubes, at least for aperiod long enough to complete the treatment of the particular workpieces being heated in the induction heating apparatus, so that suchwork does not have to be discarded.

Use of the invention is also advantageous in locations where the publicwater supply pressure is normally too low to safely provide thenecessary velocity through the tube cooling cavities and the longinsulation conduits.

The pressure controlled switch l8 may be of any suitable known typeadapted to disconnect circuit wires as at 80, in case for any reason thepressure of the water supplied to the tubes should fall verysubstantially below a predetermined value, for example 40-45 pounds persquare inch with the particular apparatus shown. The circuit wires 30may be connected in suitable known ways to control the electric powersupply to the vacuum tubes, to thus cut oil the power under the controlof the pressure switch. This pressure switch is located at a pointbetween the circulating pump and the vacuum tubes, as this is the partof the fluid circuit in which the high pressure has to be maintained toinsure the proper velocity through the tube cooling cavities. V

The flow controlled switch 25 may be of a suitable known type adapted todisconnect circuit wires 3! whenever the rate of flow from the tubesfalls below a predetermined value. The circuit wires 3| as shown may bein series with the wires 80 whereby the electric power to the tubes isunder the control of both the pressure switch and flow switch. The flowswitch is preferably located in the conduit running from the tubes tothe tank, as this is the portion of the circulating system through whichat least a predetermined flow must be constantly passing from the tubesto insure removal of suflicient heat for their protection. If anyprevious part of the fluid circuit should become blocked, even thoughthe pressure may be maintained adequate at the pressure switch l9, stillthe electric power to the tubes will be cut oil by the flow switch. Thepressure switch, in turn, insures that the power will be cut ofl upon anabnormal drop of cooling water pressure, ,even though the flow switchshould fail to operate.

If desired, to further safeguard the tubes against damage fromoverheating, a temperature control switch 82 may be inserted in thecirculating water return conduit at a point adjacent the flow switch.This temperature control switch may be of a suitable known type which,in response to a water temperature exceeding a predetermined value, willact to open the circuit between wires 33, the wires 33 being a part ofthe cally out 01f the power supply; Also in cases where the water supplybecomes shut oil and the apparatus continues to operate with thecirculation of water from and to the tank, the temperature controlswitch will serve to automatically shut down the machine when the tanktem perature becomes too high for further safe operation.

While the invention has been described in detail with respect to certainpreferred examples, it will be understood by those skilled in the artafter understanding the invention that various changes and modificationsmay be made without departing from the spirit and scope of theinvention, and it is intended therefore in the appended claims to coverall such changes and modifications.

What is claimed as new and desired to be secured by Letters Patent is:

1. Apparatus for supplying and circulating water for water-cooled powervacuum tubes, comprising a circulating pump, a mixing tank, and conduitsfor circulation of water to and from spaced points in the tank, throughthe pump and the cooling cavities of the vacuum tubes, a cool waterinlet to the system connected near the intake for the pump, and a warmwater outlet connection for discharging water from a point in the tankremote from the pump intake connection, said pump and circulatingconnections being constructed and arranged to circulate water throughthe tube cavities at a rate substantially greater than the rate ofsupply and discharge of water to and from the system, flow controlledswitch means located along the conduit which conducts warm water fromthe tube cavities to thetank, and electrical connections controlled bysaid switch means for disconnecting the vacuum tube power supply whenthe flow of said warm water is less than a predetermined rate.

2. Apparatus for supplying and circulating water for water-cooled powervacuum tubes, comprising a circulating pump, a mixing tank, and conduitsfor circulation of water to and from spaced points in the tank, throughthe pump and the cooling cavities of the vacuum tubes, 9. cool waterinlet to the system connected near the intake for the pump, and a warmwater outlet connection for discharging water from a point in the tankremote from the pump intake connection,

flow controlled switch means located along the conduit which conductswarm water from the tube cavities to the tank, electrical connectionscontrolled by said switch means for disconnecting the vacuum tube powersupply when the flow of said warm water is less than a predeterminedrate, and a pressure controlled switch means located along the conduitwhich conducts water from the pump to the tube cavities, said electricalconnections being also controlled by said pressure switch means fordisconnecting said power supply when the pressure from the pump is lessthan a predetermined value.

3. Apparatus for supplying and circulating water for water-cooled powervacuum tubes, comprising a circulating pump, a mixing tank, and conduitsfor circulation of water to and from spaced points in the tank, throughthe pump and the cooling cavities of the vacuum tubes, a cool waterinlet to the system connected near the intake for the pump, and a warmwater outlet connection for discharging water from a point in the tankremote from the pump intake connection, said pump and circulatingconnections being constructed and arranged to circulate water throughthe tube cavities at a rate substantially greater than the rate ofsupply of cool water to the system, fiow controlled switch operatingmeans and temperature controlled switch operating means both locatedalong the conduit which conducts warm water from the tube cavities tothe tank, and switches operated by said means for disconnecting thevacuum tube power supply when the flow of said warm water is at lessthan a predetermined rate or above a predetermined temperature.

4. Apparatus for supplying and circulating water for water-cooled powervacuum tubes, comprising a circulating pump, a mixing tank, and conduitsfor circulation of water to and from spaced points in the tank, throughthe pump and the cooling cavities of the vacuum tubes, a cool waterinlet to the system connected near the intake for the pump, and a warmwater outlet connection for discharging water from the tank, said pumpand circulating connections being constructed and arranged to circulatewater through the tube cavities at a rate substantially greater than therate of supply and discharge of Water to and from the system, flowcontrolled switch means located along the conduit which conducts warmwater from the tube cavities to the tank, and electrical connectionscontrolled by said switch means and adapted for disconnecting the vacuumtube power supply when the flow of said warm water is less than apredetermined rate.

5. Apparatus for supplying and circulating water for water-cooled powervacuum tubes, comprising a circulating pump, a mixing tank, and conduitsfor circulation of water to and from spaced points in the tank, throughthe pump and the cooling cavities of the vacuum tubes, a cool waterinlet to the system connected near the intake for the pump, and a warmwater outlet connection for discharging water from the tank, said pumpand circulating connections being constructed and arranged to circulatewater through the tube cavities at a rate substantially greater than therate of supply and discharge of 'water to and from the system, and apressure controlled switch means located along the conduit whichconducts water from the pump to the tube cavities, and electricalconnections controlled by said switch means adapted for disconnectingthe vacuum tube power supply when the pressure from the pump is lessthan a predetermined value.

' -WALLACE C. RUDD.

